This invention relates to an advance arrangement for use in controlling the timing of fuel delivery by a high pressure fuel injection pump intended for use in conjunction with a compression ignition internal combustion engine. More specifically the invention relates to an advance arrangement including, inter alia, a light load advance mechanism.
Although the advance arrangement associated with the fuel injection pump can adjust the timing of fuel injection in accordance, inter alia, with light load operating conditions of the associated internal combustion engine, the adjustment of a datum timing setting in relation to which adjustment by the advance arrangement takes place, is achieved by physically securing the pump to the associated engine in a predetermined angular location in relation to the pump drive mechanism. Accordingly, adjustment of the datum position is particularly inconvenient, and may be extremely difficult and time consuming in that the engine must be run, and then stopped to permit datum adjustment, and in many installations access to the pump mounting flange in order to effect adjustment of the physical position of the pump relative to the engine, is restricted.
It is an object of the present invention to provide an advance arrangement for a fuel injection pump in which the aforementioned difficulty is minimised or obviated.
In accordance with the present invention there is provided an advance arrangement for a fuel injection pump, the arrangement including a housing slidably receiving an advance piston which, in use, cooperates with the fuel injection pump to adjust the timing of fuel delivery by the pump, and, a light load piston associated with the advance piston, the housing supporting an externally accessible, adjustable abutment which cooperates with the light load piston to permit setting of a rest position of the light load piston relative to said housing and thereby to permit adjustment, from the exterior of said housing, of the datum setting from which the advance arrangement adjusts fuel injection timing.
Preferably said externally accessible, adjustable abutment is rotatable about a first axis, and includes a stop member positioned eccentrically with respect to said first axis, said stop member cooperating with said light load piston such that rotation of said adjustable abutment relative to the housing adjusts the rest position of said light load piston relative to the housing.
Preferably the axis of rotation of said adjustable abutment is at right angles to, and intersects, the axis of longitudinal movement of the light load piston.
Desirably there is provided a locking device operable to lock the abutment relative to said housing.
In a preferred embodiment a servo-piston is slidable in a bore provided in the advance piston, said light load piston is moveable relative to the advance piston against the action of a light load control spring, a servo control spring is engaged between the light load piston and the servo-piston, a light load control valve is operable to control the application of fuel to the light load piston to adjust timing under light load conditions, and an independent temperature control valve is operable to control the application of fuel to the light load piston depending upon the engine temperature to permit adjustment of the timing of fuel delivery to compensate for cold conditions.